The invention relates to a compressor system with a compressor for the supply of compressed air to a commercial vehicle having an engine possessing a turbocharger, air precompressed by the turbocharger being capable of being sucked in by the compressor via a first air feed.
The invention relates, furthermore, to a method for controlling a compressor system with a compressor for the supply of compressed air to a commercial vehicle having an engine possessing a turbocharger.
Modern commercial vehicles, as a rule, have compressed-air-operated subsystems, for example compressed-air-operated service brakes and a pneumatic spring suspension. So that the compressed-air-operated subsystems of the commercial vehicle can be supplied with sufficient compressed air, the commercial vehicle has, furthermore, a compressor for generating the compressed air.
Turbo-charged single-stage and naturally aspirating single-stage compressors are used nowadays. The advantage of the chargeable type of construction is that very large delivery quantities are available. However, it has a large spill chamber, the result of this being that, at low boost pressures of below about 0.2 bar, the delivery quantity is very small. At these low boost pressures, the delivery quantity may even be smaller than in a comparable naturally aspirating compressor. Furthermore, supercharged compressors have the disadvantage in the idling phase that they continue to convey very large air quantities, thus leading to a correspondingly high power consumption.
It is already known to restrict the boost pressure provided for a supercharged compressor to a constant value. These solutions, implemented, for example, by means of diaphragm valves, have low mechanical robustness as a consequence of the principle adopted, since mechanical control and regulating elements have to be placed in the highly pulsating air flow of the air intake path. Moreover, valves of this type themselves cause a throttling action which has an adverse effect on the conveyed air quantity particularly in the case of low boost pressures.
In order to reduce the high power losses of a supercharged compressor which occur in the idling phase, it is known to arrange what is known as a turbo-cut-off valve (TCO valve) in the feed line downstream of the compressor. This turbo-cut-off valve can reduce the conveyed air volume to zero in the idling phase of the supercharged compressor, but is highly sensitive to contamination which may occur.
The object on which the invention is based is to provide a compressor system which, particularly at low boost pressures, conveys a larger air volume.
This object is achieved by a compressor system with a compressor for the supply of compressed air to a commercial vehicle having an engine possessing a turbocharger, air precompressed by the turbocharger being capable of being sucked in by the compressor via a first air feed. Non-precompressed ambient air can be sucked in by the compressor via a second air feed. By providing a second air feed, via which non-precompressed ambient air can be sucked in by the compressor, a compressor which is optimized for the aspiration of non-precompressed ambient air can be used in the compressor system. This leads to a marked increase in the conveyed air quantity even at low boost pressures.
It is advantageous, in this respect, that a charge-air valve device is arranged in the first air feed. The compressor can be protected from excessively high boost pressures by the charge-air valve device in the first air feed. If the boost pressure provided by the turbocharger overshoots an adjustable boost-pressure threshold, the charge-air valve device can shut off the first air feed.
It is particularly preferable, furthermore, that an ambient-air valve device is arranged in the second air feed. By the ambient-air valve device being arranged in the second air feed, non-precompressed ambient air can be fed to the compressor when the boost pressure provided by the turbocharger overshoots the adjustable boost-pressure threshold. In particular, the ambient-air valve device can close the second air feed as long as the boost pressure provided by the turbo charger does not overshoot the boost-pressure threshold.
There is expediently provision made for a pressure sensor to be arranged in the first air feed in order to determine the boost pressure provided by the turbocharger. By arranging a pressure sensor in the first air feed, the boost pressure provided by the turbocharger can be determined directly. The signal generated by the pressure sensor is therefore suitable for serving as a basis for the direct or indirect control of the charge-air valve device or of the ambient-air valve device.
It is contemplated that the compressor includes a spill chamber connectable via a valve device. By providing a connectable spill chamber, pressure peaks which occur particularly at high boost pressures can be reduced. Thus, in particular, the selected adjustable boost-pressure threshold can be higher, without the compressor being overloaded by excessively high pressures.
Advantageously, there is provision for the compressor system to have an electronic control apparatus for the control of functions of the compressor system. An electronic control apparatus can, in a simple way, switch various electrically actuable functions, in particular electrically actuable or pilot-controllable valve devices.
In this case, provision may be made for the electronic control apparatus to include a connection to a CAN bus, and for the electronic control apparatus to receive via the CAN bus the value of the current boost pressure provided by the turbocharger or raw data for calculating the current boost pressure. By being connected to the CAN bus of the vehicle, the electronic control apparatus can ascertain or determine the boost pressure provided by the turbocharger independently of specific sensors.
The generic method is developed further in that, below an adjustable boost-pressure threshold, precompressed air provided by the turbocharger is sucked in by the compressor via a first air feed, and in that, above the adjustable boost-pressure threshold, non-precompressed ambient air is sucked in by the compressor via a second air feed. Thus, the advantages and special features of the compressor system according to the invention are also implemented within the framework of a method for operating a compressor system.
This also applies to the particularly preferred embodiments, specified below, of the method according to the invention.
This is expediently developed further in that, below the adjustable boost-pressure threshold, an ambient-air valve device closes the second air feed. There is in this case expediently provision made for a charge-air valve device to close the first air feed above the adjustable boost-pressure threshold.
It is also contemplated that a valve device connects a spill chamber above an adjustable spill-chamber boost-pressure threshold.
In particular, there may be provision for the boost pressure to be determined via a pressure sensor. There may, however, also be provision made for the boost pressure to be determined from CAN bus data and/or to be transmitted via a CAN bus.
In addition, the first air feed may be closed by the charge-air valve device and the second air feed may be closed by the ambient-air valve device in order to put the compressor into an energy-saving operating state. By the first air feed and the second air feed being shut off simultaneously, the air volume conveyed by the compressor is reduced to zero.
There may be provision, in this respect, for the charge-air valve device and/or the ambient-air valve device to limit an intake underpressure of the compressor by way of a residual leak. By means of a small residual leak which restricts the intake underpressure generated by the compressor, an oil ejection from the compressor due to oil suction can be reduced.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.